How would I make each one of these faces a separate "plank?"
Here is a non destructive technique I like to use that works for simple cases, when you don't want to break the model apart or need to separate into different objects.


Add an Edge Split modifier to your base mesh
Solidify it a desired distance
Now add a Bevel modifier and limit it to Angle
Enter Edit Mode, select and the desired edges
Press Ctrl + E and Mark Sharp
Adjust Bevel distance as desired, if necessary disable Clamp